P. Treadwell et al. (eds.)Atlas of Adolescent Dermatologyhttps://doi.org/10.1007/978-3-030-58634-8_7

7. Lice

Julie Prendiville¹

(1)

Department of Pediatrics, University of British Columbia, Vancouver, BC, Canada

Julie Prendiville

Email: jprendiville@sidra.org

Keywords

Head licePubic liceNitsPermethrinIvermectin

7.1 Introduction

Lice infestation in children and adolescents is mainly caused by the head louse (Pediculus humanus capitis). The pubic or crab louse (Phthirus pubis) is transmitted by sexual contact or by co-sleeping. Infestation with the clothing louse (P. humanus humanus) occurs in homeless populations.

7.2 Epidemiology

Head louse infestation (pediculosis capitis) is common in school-aged populations worldwide. All socioeconomic groups are affected. It is spread primarily by head-to-head transmission, and possibly also from fomites. There is an apparent increased prevalence in girls. Head lice may be associated with infection of the scalp by Staphylococcus aureus and/or Group A streptococcus.

7.3 Clinical Findings

Pruritus is the main symptom but can be absent initially. Head lice may also present with impetigo of the scalp (Fig. 7.1) and occipital/cervical lymphadenopathy. Eggs, or nits, are found cemented to the hair shafts, often over the occiput and behind the ears. Live lice may sometimes be observed. Nits in the pubic or axillary hair, and on the eyelashes, are an indication of crab lice (Fig. 7.2).

../images/446896_1_En_7_Chapter/446896_1_En_7_Fig1_HTML.png — Fig. 7.1
Head lice – with nits on hairs and excoriations of the scalp

../images/446896_1_En_7_Chapter/446896_1_En_7_Fig2_HTML.jpg — Fig. 7.2
Crab louse attached to a hair

7.4 Laboratory

Lice found in the hair or after combing may be identified by simple magnification, or by light microscopy. Nits can be distinguished from hair casts or “pseudonits” by dermoscopy or light microscopy.

7.5 Treatment

Over-the-counter treatments for head lice include pyrethrin shampoos, 1% permethrin lotion, isopropyl myristate/cyclomethicone, and dimethicone lotion. Topical medications available by prescription are ivermectin 0.5%, benzyl alcohol 5%, spinosad 0.9%, and malathion 0.5%. Nit combing every 2–3 days after treatment is often recommended to prevent or identify reinfestation.

Pubic or crab lice are treated with 1% permethrin or 0.5% ivermectin lotion. Petrolatum may be applied to the eyelashes, if involved.

7.6 Prognosis

Reinfestation may occur due to medication-resistant lice or further exposure.